refactor(storage): remove lifetime on iterators

[lmatz]

What's changed and what's your intention?

Remove all the lifetime associated with iterators defined in Hummock.

This PR conflicts with PR #1928 on use XXX statements only at one location. It seems #1928 is ready and this PR will wait for it to be merged first.

After this refactoring, we can bound the trait StateStoreIter by 'static. This will bypass the compiler limitation described in #1930 when Send is used to bound NextFuture in StateStoreIter.

Refer to a related PR or issue link (optional)

#1930

[codecov]

Codecov Report

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The diff coverage is 100.00%.

❗ Current head a11a775 differs from pull request most recent head fdc8832. Consider uploading reports for the commit fdc8832 to get more accurate results

@@           Coverage Diff           @@
##             main    #1956   +/-   ##
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  Coverage        ?   70.92%           
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  Files           ?      619           
  Lines           ?    80106           
  Branches        ?        0           
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  Hits            ?    56815           
  Misses          ?    23291           
  Partials        ?        0           

Flag	Coverage Δ
rust	70.92% <100.00%> (?)

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Impacted Files	Coverage Δ
src/storage/src/hummock/iterator/merge.rs	95.77% <ø> (ø)
src/storage/src/hummock/iterator/mod.rs	100.00% <ø> (ø)
src/storage/src/hummock/iterator/reverse_merge.rs	93.67% <ø> (ø)
src/storage/src/hummock/compactor.rs	67.44% <100.00%> (ø)
src/storage/src/hummock/iterator/merge_inner.rs	83.78% <100.00%> (ø)
src/storage/src/hummock/iterator/reverse_user.rs	95.72% <100.00%> (ø)
src/storage/src/hummock/iterator/test_utils.rs	76.53% <100.00%> (ø)
src/storage/src/hummock/iterator/user.rs	94.40% <100.00%> (ø)
src/storage/src/hummock/state_store.rs	70.50% <100.00%> (ø)
src/storage/src/hummock/test_utils.rs	81.37% <100.00%> (ø)

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